In the wake of recent stringent emissions controls and high fuel prices, it has become increasingly important to provide precise control over the combustion process in internal combustion engines. The invention is discussed in the context of diesel engines.
A typical fuel injection pump for a diesel engine comprises a pressurized fuel source, a plunger valve which meters the fuel to each cylinder's fuel injector, a camshaft operating the plungers up and down, and a rack arrangement for rotationally positioning the plungers.
The camshaft is driven in syntony (at the same speed) with an engine fuel pump drive shaft, but at a variable advance angle thereto. The advance angle determines the onset of injection.
The rack is typically moved within a limited range of linear positions to determine a limited range of plunger rotational positions by a throttle control and a flyweight arrangement driven off of the camshaft. The rotational position of the plungers determines the end of fuel metering, and hence the fuel quantity delivered.
A flyweight arrangement involves many moving parts.
U.S. Pat. No. 4,502,537 (Voss, 1985) discloses (in FIG. 6) positioning the pump rack with a stepping motor actuator (106), and having a reference stop (230) at the zero throttle position to initialize the stepper motor by causing it to move the pump rack linkage (202) in the direction of the reference stop. Reinitialization is assured at this point by providing as many pulses to the stepper motor as there are in the full stroke of the motor (see column 11, lines 36-50).
U.S. Pat. No. 4,570,588 (Herdin, et. al., 1986) discloses (in FIG. 1) positioning a control rod (2) with a stepping motor (10) through the intermediary of a resiliently yieldable coupling comprising a coupling plate (11) fixed to the output shaft of the stepping motor and driving through coupling pins (12,12a) and a tension spring (14), a camwheel (7) that urges the control rod. The spring (14) acts as an energy storage device to alleviate the possibility of a phase shift (position error) between the stepping motor and the control rod. This possibility may arise if the control rod load exceeds the stepping motor output.
European Patent Application No. 0,069,111 (Stipek, et. al., 1983) discloses positioning a control rod (17) with a stepper motor (4) via a pinion gear (5) on the motor moving a toothed rack (6) that is coupled to the control rod via a double-acting resilient linkage that involves a prestressed compression spring (11).